1. Field of the Invention
The present invention relates to an electrostatic image developing toner and a two-component electrostatic image developer.
2. Description of the Related Art
Increasing printing speed in digital printing which outputs images through electrophotographic processes requires toners to have higher low-temperature fixability during fixation of toner images. As toners having higher low-temperature fixability, crystalline resin-including toners have recently been in development. In addition, as toners having both low-temperature fixability and thermal storage stability (i.e., blocking resistance), toners containing a crystalline resin and amorphous resin have been proposed (see Japanese Unexamined Patent Application Publication No. 2011-197659, for example).
Digital printing, which can output various prints each of which is outputted in a small number, is much more advantageous than offset printing, which should make proofs for printing. In this context, requirement for digital printing is to output various prints successively from ones having high printing rates (high coverage rates), such as photobooks which desirably have high image quality, to ones having low printing rates (low coverage rates), such as address labels of direct mails.
Printing images having high coverage rate consumes large amount of a toner. Thus, much of the toner comes into contact with a carrier and an external additive relocates onto the surface of the carrier, resulting in a ready change in charge level of the toner. In contrast, since printing images having low coverage rate refreshes a toner at relatively low frequencies, the toner undergoes larger stress. Consequently, an external additive is embedded and charge level of the toner decreases, resulting in a decrease in image quality of output images.
Digital printing also requires to retain the charge of the toner at a proper level and to stably output high quality images under conditions such as high temperature and humidity (HH) and low temperature and humidity (LL) environments.
As described, the charge level of a toner should be stable under various conditions including printing environments and/or coverage rates set by users. Thus, ways for achieving such stability have been studied (see Japanese Unexamined Patent Application Publication No. 2013-235046, for example).